Method of electroplating photoresist defined features from copper electroplating baths containing reaction products of alpha amino acids and bisepoxides

ABSTRACT

Electroplating methods enable the plating of photoresist defined features which have substantially uniform morphology. The electroplating methods include copper electroplating baths with reaction products of α-amino acids and bisepoxides to electroplate the photoresist defined features. Such features include pillars, bond pads and line space features.

FIELD OF THE INVENTION

The present invention is directed to a method of electroplatingphotoresist defined features from copper electroplating baths whichinclude reaction products of α-amino acids and bisepoxides. Morespecifically, the present invention is directed to a method ofelectroplating photoresist defined features from copper electroplatingbaths which include reaction products of α-amino acids and bisepoxideswhere the photoresist defined features have substantially uniformsurface morphology.

BACKGROUND OF THE INVENTION

Photoresist defined features include copper pillars and redistributionlayer wiring such as bond pads and line space features for integratedcircuit chips and printed circuit boards. The features are formed by theprocess of lithography where a photoresist is applied to a substratesuch as a semiconductor wafer chip often referred to as a die inpackaging technologies, or epoxy/glass printed circuit boards. Ingeneral, the photoresist is applied to a surface of the substrate and amask with a pattern is applied to the photoresist. The substrate withthe mask is exposed to radiation such as UV light. Typically thesections of the photoresist which are exposed to the radiation aredeveloped away or removed exposing the surface of the substrate.Depending on the specific pattern of the mask an outline of a circuitline or aperture may be formed with the unexposed photoresist left onthe substrate forming the walls of the circuit line pattern orapertures. The surface of the substrate includes a metal seed layer orother conductive metal or metal alloy material which enables the surfaceof the substrate conductive. The substrate with the patternedphotoresist is then immersed in a metal electroplating bath, typically acopper electroplating bath, and metal is electroplated in the circuitline pattern or apertures to form features such as pillars, bond pads orcircuit lines, i.e., line space features. When electroplating iscomplete, the remainder of the photoresist is stripped from thesubstrate with a stripping solution and the substrate with thephotoresist defined features is further processed.

Pillars, such as copper pillars, are typically capped with solder toenable adhesion as well as electrical conduction between thesemiconductor chip to which the pillars are plated and a substrate. Sucharrangements are found in advanced packaging technologies. Solder cappedcopper pillar architectures are a fast growing segment in advancedpackaging applications due to improved input/output (I/O) densitycompared to solder bumping alone. A copper pillar bump with thestructure of a non-reflowable copper pillar and a reflowable solder caphas the following advantages: (1) copper has low electrical resistanceand high current density capability; (2) thermal conductivity of copperprovides more than three times the thermal conductivity of solder bumps;(3) can improve traditional BGA CTE (ball grid array coefficient ofthermal expansion) mismatch problems which can cause reliabilityproblems; and (4) copper pillars do not collapse during reflow allowingfor very fine pitch without compromising stand-off height.

Of all the copper pillar bump fabrication processes, electroplating isby far the most commercially viable process. In the actual industrialproduction, considering the cost and process conditions, electroplatingoffers mass productivity and there is no polishing or corrosion processto change the surface morphology of copper pillars after the formationof the copper pillars. Therefore, it is particularly important to obtaina smooth surface morphology by electroplating. The ideal copperelectroplating chemistry and method for electroplating copper pillarsyields deposits with excellent uniformity, flat pillar shape andvoid-free intermetallic interface after reflow with solder and is ableto plate at high deposition rates to enable high wafer through-out.However, development of such plating chemistry and method is a challengefor the industry as improvement in one attribute typically comes at theexpense of another. Copper pillar based structures have already beenemployed by various manufacturers for use in consumer products such assmart phones and PCs. As Wafer Level Processing (WLP) continues toevolve and adopt the use of copper pillar technology, there will beincreasing demand for copper plating baths and methods with advancedcapabilities that can produce reliable copper pillar structures.

Similar problems of morphology are also encountered with the metalelectroplating of redistribution layer wiring. Defects in the morphologyof bond pads and line space features also compromise the performance ofadvanced packaging articles. Accordingly, there is a need for a copperelectroplating methods and chemistries which provide copper photoresistdefined features where the features have substantially uniform surfacemorphology.

SUMMARY OF THE INVENTION

A method comprising: a) providing a substrate comprising a layer ofphotoresist, wherein the layer of photoresist comprises a plurality ofapertures; b) providing a copper electroplating bath comprising one ormore reaction products of one or more α-amino acids and one or morebisepoxides; an electrolyte; one or more accelerators; and one or moresuppressors; c) immersing the substrate comprising the layer ofphotoresist with the plurality of apertures in the copper electroplatingbath; and d) electroplating a plurality of copper photoresist definedfeatures in the plurality of apertures, the plurality of photoresistdefined features comprise an average % TIR of −5% to −1%.

Copper electroplating baths include a reaction product of one or moreα-amino acids and one or more bisepoxides, a electrolyte, one or moresources of copper ions, one or more accelerators and one or moresuppressors in sufficient amounts to electroplate copper photoresistdefined features having an average % TIR of −5% to −1%.

A plurality of photoresist defined features on a substrate comprising anaverage % TIR of −5% to −1% and an average % WID of 12% to 15%.

The copper electroplating methods and baths provide copper photoresistdefined features which have a substantially uniform morphology and aresubstantially free of nodules. The copper pillars and bond pads have asubstantially flat profile. The copper electroplating baths and methodsenable an average % TIR to achieve the desired morphology.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a SEM of a copper pillar at 300× electroplated from a copperelectroplating bath containing a reaction product of L-arginine andglycerol diglycidyl ether.

FIG. 2 is a SEM of a copper pillar at 300× electroplated from a copperelectroplating bath containing a conventional leveler compound which isa reaction product of 2-methylquinolin-4-amine, aminoethyl pyridine andglycerol diglycidyl ether.

DETAILED DESCRIPTION OF THE INVENTION

As used throughout this specification the following abbreviations shallhave the following meanings unless the context clearly indicatesotherwise: A=amperes; A/dm²=amperes per square decimeter=ASD; °C.=degrees Centigrade; UV=ultraviolet radiation; g=gram; ppm=parts permillion=mg/L; L=liter, μm=micron=micrometer; mm=millimeters;cm=centimeters; DI=deionized; mL=milliliter; mol=moles; mmol=millimoles;Mw=weight average molecular weight; Mn=number average molecular weight;SEM=scanning electron microscope; FIB=focus ion beam; WID=within-die;TIR=total indicated runout=total indicator reading=full indicatormovement=FIM; RDL=redistribution layer; and Avg.=average.

As used throughout this specification, the term “plating” refers tometal electroplating. “Deposition” and “plating” are usedinterchangeably throughout this specification. “Accelerator” refers toan organic additive that increases the plating rate of theelectroplating bath. “Suppressor” refers to an organic additive thatsuppresses the plating rate of a metal during electroplating. The term“array” means an ordered arrangement. The term “moiety” means a part ofa molecule or polymer that may include either whole functional groups orparts of functional groups as substructures. The terms “moiety” and“group” are used interchangeably throughout the specification. The term“aperture” means opening, hole or gap. The term “morphology” means theform, shape and structure of an article. The term “total indicatorrunout” or “total indicator reading” is the difference between themaximum and minimum measurements, that is, readings of an indicator, onplanar, cylindrical, or contoured surface of a part, showing its amountof deviation from flatness, roundness (circularity), cylindricity,concentricity with other cylindrical features or similar conditions. Theterm “profilometry” means the use of a technique in the measurement andprofiling of an object or the use of a laser or white lightcomputer-generated projections to perform surface measurements of threedimensional objects. The term “pitch” means a frequency of featurepositions from each other on a substrate. The term “normalizing” means arescaling to arrive at values relative to a size variable such as aratio as % TIR. The term “average” means a number expressing the centralor typical value of a parameter. The term “parameter” means a numericalor other measurable factor forming one of a set that defines a system orsets the conditions of operation. The articles “a” and “an” refer to thesingular and the plural.

All numerical ranges are inclusive and combinable in any order, exceptwhere it is clear that such numerical ranges are constrained to add upto 100%.

Methods and baths for electroplating copper photoresist defined featuresof the present invention enable an array of photoresist defined featureshaving an average % TIR such that the features have a morphology whichis substantially smooth, free of nodules and with respect to pillars,bond pads and line space features have substantially flat profiles. Thephotoresist defined features of the present invention are electroplatedwith photoresist remaining on the substrate and extend beyond the planeof the substrate. This is in contrast to dual damascene and printedcircuit board plating which typically do not use photoresist to definefeatures which extend beyond the plane of the substrate but are inlaidinto the substrate. An important difference between photoresist definedfeatures and damascene and printed circuit board features is that withrespect to the damascene and printed circuit boards the plating surfaceincluding the sidewalls are all conductive. The dual damascene andprinted circuit board plating baths have a bath formulation thatprovides bottom-up or super-conformal filling, with the bottom of thefeature plating faster than the top of the feature. In photoresistdefined features, the sidewalls are non-conductive photoresist andplating only occurs at the feature bottom with the conductive seed layerand proceeds in a conformal or same plating speed everywhere deposition.

While the present invention is substantially described with respect tomethods of electroplating copper pillars having a circular morphology,the present invention also applies to other photoresist defined featuressuch as bond pads and line space features. In general, the shapes of thefeatures may be, for example, oblong, octagonal and rectangular inaddition to circular or cylindrical. The methods of the presentinvention are preferably for electroplating copper cylindrical pillars.

The copper electroplating methods provide an array of copper photoresistdefined features, such as copper pillars, with an average % TIR of −5%to −1%, preferably from −4% to −2%, even more preferably −3%.

In general, the average % TIR for an array of photoresist definedfeatures on a substrate involves determining the % TIR of individualfeatures from the array of features on the single substrate andaveraging them. Typically, the average % TIR is determined bydetermining the % TIR for individual features of a region of low densityor larger pitch and the % TIR for individual features of a region ofhigh density or smaller pitch on the substrate and averaging the values.By measuring the % TIR of a variety of individual features, the average% TIR becomes representative of the whole substrate.

The % TIR may be determined by the following equation:% TIR=[height_(center)−height_(edge)]/height_(max)×100where height_(center) is the height of a pillar as measured along itscenter axis and height_(edge) is the height of the pillar as measuredalong its edge at the highest point on the edge. Height_(max) is theheight from the bottom of the pillar to its highest point on its top.Height_(max) is a normalizing factor.

Individual feature TIRs may be determined by the following equation:TIR=height_(center)−height_(edge),where height_(center) and height_(edge) are as defined above.

In addition, the copper electroplating methods and baths may provide anarray of copper photoresist defined features with a % WID of 12% to 15%,preferably from 13% to 15% and even more preferably 15%. The % WID orwithin-die may be determined by the following equation:% WID=1/2×[(height_(max)−height_(min))/height_(avg)]×100where height_(max) is the height of the tallest pillar of an array ofpillars electroplated on a substrate as measured at the tallest part ofthe pillar. Height_(min) is the height of the shortest pillar of anarray of pillars electroplated on the substrate as measured at thetallest part of the pillar. Height_(avg) is the average height of all ofthe pillars electroplated on the substrate.

Most preferably, the methods of the present invention provide an arrayof photoresist defined features on a substrate where there is a balancebetween the average % TIR and % WID such that the average % TIR rangesfrom −5% to −1% and the % WID ranges from 12% to 15% with the preferredranges as disclosed above.

The parameters of the pillars for determining TIR, % TIR and % WID maybe measured using optical profilometry such as with a white light LEICADCM 3D or similar apparatus. Parameters such as pillar height and pitchmay be measured using such devices.

In general, the copper pillars electroplated from the copperelectroplating baths may have aspect ratios of 3:1 to 1:1 or such as 2:1to 1:1. RDL type structure may have aspect ratios as large as 1:20(height:width).

Amino acids include both natural and synthetic amino acids and saltsthereof, such as alkali metal salts. Amino acids include an amino group,a carboxyl group, a hydrogen atom and an amino acid side chain moietyall bonded, in the case of an α-amino acid, to a single carbon atom thatis referred to as an a-carbon. Preferably the amino acids are chosenfrom α-amino acids.

α-Amino acids include, but are not limited to those disclosed in Table 1below:

TABLE 1 Amino Acid Structure Amino Acid

Glycine

Alanine

Valine

Leucine

Isoleucine

Lysine

Arginine

Histidine

Aspartic acid

Asparagine

Glutamine

Phenylalanine

Tyrosine

Trytophan

Cysteine

Methionine

Serine

ornithine

3-Phenylserine

Threonine

L-DOPA

Norleucine

PenicillaminePreferably the α-amino acids are arginine and lysine. More preferablythe α-amino acid is arginine.

Preferably bisepoxide compounds include compounds having formula:

where R₁ and R₂ are independently chosen from hydrogen and (C₁-C₄)alkyl,A=O((CR₃R₄)_(m)O)_(n) or (CH₂)_(y), each R₃ and R₄ is independentlychosen from hydrogen, methyl, or hydroxyl, m=1-6, n=1-20 and y=0-6. R₁and R₂ are preferably independently chosen from hydrogen and(C₁-C₂)alkyl. More preferably R₁ and R₂ are both hydrogen. It ispreferred that m=2-4. Preferably n=1-10, more preferably n=1. Preferablyy=0-4 and more preferably 1-4. When A=(CH₂)_(y) and y=0, then A is achemical bond.

Bisepoxides where A=O((CR₃R₄)_(m)O)_(n) have a formula:

where R₁, R₂, R₃, R₄, m and n are as defined above. Preferably, R₁ andR₂ are hydrogen. Preferably R₃ and R₄ are independently chosen fromhydrogen, methyl and hydroxyl. More preferably R₃ is hydrogen, and R₄ ishydrogen or hydroxyl. When R₄ is hydroxyl and m=3, it is preferred thatonly one R₄ is hydroxyl with the remainder hydrogen. Preferably m is aninteger of 2-4 and n is an integer of 1-2. More preferably m is 3-4 andn is 1. Even more preferably m=3 and n=1.

Compounds of formula (II) include, but are not limited to,1,4-butanediol diglycidyl ether, ethylene glycol diglycidyl ether,di(ethylene glycol) diglycidyl ether, 1,2,7,8-diepoxyoctane,1,2,5,6-diepoxyhexane, 1,2,7,8-diepoxyoctane, 1,3-butandiol diglycidylether, glycerol diglycidyl ether, neopentyl glycol diglycidyl ether,propylene glycol diglycidyl ether, di(propylene glycol) diglycidylether, poly(ethylene glycol) diglycidyl ether compounds andpoly(propylene glycol) diglycidyl ether compounds.

Compounds specific for formula (III) include, but are not limited to1,4-butanediol diglycidyl ether, ethylene glycol diglycidyl ether,di(ethylene glycol) diglycidyl ether, 1,3-butandiol diglycidyl ether,glycerol diglycidyl ether, neopentyl glycol diglycidyl ether, propyleneglycol diglycidyl ether, di(propylene glycol) diglycidyl ether,poly(ethylene glycol) diglycidyl ether compounds and poly(propyleneglycol) diglycidyl ether compounds. Most preferably the compound offormula (III) is glycerol diglycidyl ether.

Additional preferred bisepoxides include bisepoxides having cycliccarbon moieties such as those having six carbon cyclic moieties. Suchbisepoxides include, but are not limited to 1,4-cyclohexanedimethanoldiglycidyl ether and resorcinol diglycidyl ether.

The order of addition of reactants to a reaction vessel may vary,however, preferably, one or more α-amino acids are dissolved in water at80° C. with dropwise addition of one or more bisepoxides. For reactantswith poor water solubility small amounts of sulfuric acid or sodiumhydroxide are added prior to epoxy addition. The temperature of theheating bath is then increased from 80° C. to 95° C. Heating withstirring is done for 2 hours to 4 hours. After an additional 6-12 hoursof stirring at room temperature, the resulting reaction product isdiluted with water. The reaction product may be used as-is in aqueoussolution, may be purified or may be isolated as desired. Typically, themolar ratio of the α-amino acid to the bisepoxide is from 0.1:10 to10:0.1. Preferably, the molar ratio is from 1:5 to 5:1 and morepreferably from 1:2 to 2:1. Other suitable ratios of α-amino acid tobisepoxide may be used to prepare the present reaction products.

Suitable copper ion sources are copper salts and include withoutlimitation: copper sulfate; copper halides such as copper chloride;copper acetate; copper nitrate; copper tetrafluoroborate; copperalkylsulfonates; copper aryl sulfonates; copper sulfamate; copperperchlorate and copper gluconate. Exemplary copper alkane sulfonatesinclude copper (C₁-C₆)alkane sulfonate and more preferably copper(C₁-C₃)alkane sulfonate. Preferred copper alkane sulfonates are coppermethanesulfonate, copper ethanesulfonate and copper propanesulfonate.Exemplary copper arylsulfonates include, without limitation, copperbenzenesulfonate and copper p-toluenesulfonate. Mixtures of copper ionsources may be used. One or more salts of metal ions other than copperions may be added to the present electroplating baths. Preferably, thecopper salt is present in an amount sufficient to provide an amount ofcopper ions of 30 to 60 g/L of plating solution. More preferably theamount of copper ions is from 40 to 50 g/L.

The electrolyte useful in the present invention may be alkaline oracidic. Preferably the electrolyte is acidic. Preferably, the pH of theelectrolyte is ≤2. Suitable acidic electrolytes include, but are notlimited to, sulfuric acid, acetic acid, fluoroboric acid, alkanesulfonicacids such as methanesulfonic acid, ethanesulfonic acid, propanesulfonicacid and trifluoromethane sulfonic acid, aryl sulfonic acids such asbenzenesulfonic acid, p-toluenesulfonic acid, sulfamic acid,hydrochloric acid, hydrobromic acid, perchloric acid, nitric acid,chromic acid and phosphoric acid. Mixtures of acids may beadvantageously used in the present metal plating baths. Preferred acidsinclude sulfuric acid, methanesulfonic acid, ethanesulfonic acid,propanesulfonic acid, hydrochloric acid and mixtures thereof. The acidsmay be present in an amount in the range of 1 to 400 g/L. Electrolytesare generally commercially available from a variety of sources and maybe used without further purification.

Such electrolytes may optionally contain a source of halide ions.Typically chloride ions or bromide ions are used. Exemplary chloride ionsources include copper chloride, tin chloride, sodium chloride,potassium chloride and hydrochloric acid. Exemplary bromide ion sourcesare sodium bromide, potassium bromide and hydrogen bromide. A wide rangeof halide ion concentrations may be used in the present invention.Typically, the halide ion concentration is in the range of 0 to 100 ppmbased on the plating bath, preferably from 50 to 80 ppm. Such halide ionsources are generally commercially available and may be used withoutfurther purification.

The plating baths typically contain an accelerator. Any accelerators(also referred to as brightening agents) are suitable for use in thepresent invention. Such accelerators are well-known to those skilled inthe art. Accelerators include, but are not limited to,N,N-dimethyl-dithiocarbamic acid-(3-sulfopropyl)ester;3-mercapto-propylsulfonic acid-(3-sulfopropyl)ester;3-mercapto-propylsulfonic acid sodium salt; carbonicacid,dithio-O-ethylester-S-ester with 3-mercapto-1-propane sulfonic acidpotassium salt; bis-sulfopropyl disulfide; bis-(sodiumsulfopropyl)-disulfide; 3-(benzothiazolyl-S-thio)propyl sulfonic acidsodium salt; pyridinium propyl sulfobetaine;1-sodium-3-mercaptopropane-1-sulfonate; N,N-dimethyl-dithiocarbamicacid-(3-sulfoethyl)ester; 3-mercapto-ethyl propylsulfonicacid-(3-sulfoethyl)ester; 3-mercapto-ethylsulfonic acid sodium salt;carbonic acid-dithio-O-ethylester-S-ester with 3-mercapto-1-ethanesulfonic acid potassium salt; bis-sulfoethyl disulfide;3-(benzothiazolyl-S-thio)ethyl sulfonic acid sodium salt; pyridiniumethyl sulfobetaine; and 1-sodium-3-mercaptoethane-1-sulfonate.Accelerators may be used in a variety of amounts. In general,accelerators are used in an amount in a range of 0.1 ppm to 1000 ppm.

Suitable suppressors include, but are not limited to, polypropyleneglycol copolymers and polyethylene glycol copolymers, including ethyleneoxide-propylene oxide (“EO/PO”) copolymers and butyl alcohol-ethyleneoxide-propylene oxide copolymers. The weight average molecular weight ofthe suppressors may range from 800-15000, preferably 1000-15000. Whensuch suppressors are used, they are preferably present in a range of 0.5g/L to 15 g/L based on the weight of the composition, and morepreferably from 1 g/L to 5 g/L.

In general, the reaction products have a number average molecular weight(Mn) of 200 to 100,000, typically from 300 to 50,000, preferably from500 to 30,000, although reaction products having other Mn values may beused. Such reaction products may have a weight average molecular weight(Mw) value in the range of 1000 to 50,000, typically from 5000 to30,000, although other Mw values may be used.

The amount of the reaction product used in the copper electroplatingbaths for plating photoresist defined features, preferably copperpillars, may range from 0.25 ppm to 20 ppm, preferably from 0.25 ppm to10 ppm, more preferably from 0.25 ppm to 5 ppm, and even more preferablyfrom 0.25 ppm to 2 ppm based on the total weight of the plating bath.

The electroplating compositions may be prepared by combining thecomponents in any order. It is preferred that the inorganic componentssuch as source of metal ions, water, electrolyte and optional halide ionsource are first added to the bath vessel, followed by the organiccomponents such as leveling agent, accelerator, suppressor, and anyother organic component.

The aqueous copper electroplating baths may optionally contain aconventional leveling agent provided such the leveling agent does notsubstantially compromise the morphology of the copper features. Suchleveling agents may include those disclosed in U.S. Pat. No. 6,610,192to Step et al., U.S. Pat. No. 7,128,822 to Wang et al., U.S. Pat. No.7,374,652 to Hayashi et al. and U.S. Pat. No. 6,800,188 to Hagiwara etal. However, it is preferred that such leveling agents are excluded fromthe baths.

Typically, the plating baths may be used at any temperature from 10 to65° C. or higher. Preferably, the temperature of the plating compositionis from 15 to 50° C. and more preferably from 20 to 40° C.

In general, the copper electroplating baths are agitated during use. Anysuitable agitation method may be used and such methods are well-known inthe art. Suitable agitation methods include, but are not limited to: airsparging, work piece agitation, and impingement.

Typically, a substrate is electroplated by contacting the substrate withthe plating bath. The substrate typically functions as the cathode. Theplating bath contains an anode, which may be soluble or insoluble.Potential is applied to the electrodes. Current densities may range from0.25 ASD to 40 ASD, preferably 1 ASD to 20 ASD, more preferably from 4ASD to 18 ASD.

While the method of the present invention may be used to electroplatephotoresist defined features such as pillars, bonding pads and linespace features, the method is described in the context of plating copperpillars which is the preferred feature of the present invention.Typically, the copper pillars may be formed by first depositing aconductive seed layer on a substrate such as a semiconductor chip ordie. The substrate is then coated with a photoresist material and imagedto selectively expose the photoresist layer to radiation such as UVradiation. The photoresist layer may be applied to a surface of thesemiconductor chip by conventional processes known in the art. Thethickness of the photoresist layer may vary depending on the height ofthe features. Typically the thickness ranges from 1 μm to 250 μm. Apatterned mask is applied to a surface of the photoresist layer. Thephotoresist layer may be a positive or negative acting photoresist. Whenthe photoresist is positive acting, the portions of the photoresistexposed to the radiation are removed with a developer such as analkaline developer. A pattern of a plurality of apertures is formed onthe surface which reaches all the way down to the seed layer on thesubstrate or die. The pitch of the pillars may range from 20 μm to 400μm. Preferably the pitch may range from 40 μm to 250 μm. The diametersof the apertures may vary depending on the diameter of the feature. Thediameters of the apertures may range from 2 μm to 200 μm, typically from10 μm to 75 μm. The entire structure may then be placed in a copperelectroplating bath containing one or more of the reaction products ofthe present invention. Electroplating is done to fill at least a portionof each aperture with a copper pillar with a substantially flat top.Electroplating is vertical fill without horizontal plating orsuperfilling. The entire structure with the copper pillars is thentransferred to a bath containing solder, such as a tin solder or tinalloy solder such as a tin/silver or tin/lead alloy and a solder bump iselectroplated on the substantially flat surface of each copper pillar tofill portions of the apertures. The remainder of the photoresist isremoved by conventional means known in the art leaving an array ofcopper pillars with solder bumps on the die. The remainder of the seedlayer not covered by pillars is removed through etching processes wellknown in the art. The copper pillars with the solder bumps are placed incontact with metal contacts of a substrate such as a printed circuitboard, another wafer or die or an interposer which may be made oforganic laminates, silicon or glass. The solder bumps are heated byconventional processes known in the art to reflow the solder and jointhe copper pillars to the metal contacts of the substrate. Conventionalreflow processes for reflowing solder bumps may be used. An example of areflow oven is FALCON 8500 tool from Sikiama International, Inc. whichincludes 5 heating and 2 cooling zones. Reflow cycles may range from1-5. The copper pillars are both physically and electrically contactedto the metal contacts of the substrate. An underfill material may thenbe injected to fill space between the die, the pillars and thesubstrate. Conventional underfills which are well known in the art maybe used.

FIG. 1 is a SEM of a copper pillar of the present invention havingcylindrical morphologies with a base and substantially flat top forelectroplating solder bumps. During reflow solder is melted to obtain asmooth surface. If pillars are too domed during reflow, the solder maymelt and flow off the sides of the pillar and then there is not enoughsolder on the top of the pillar for subsequent bonding steps. If thepillar is too dished as shown in FIG. 2, material left from the copperbath which was used to electroplate the pillar may be retained in thedished top and contaminate the solder bath, thus shortening the life ofthe solder bath.

To provide a metal contact and adhesion between the copper pillars andthe semiconductor die during electroplating of the pillars, an underbumpmetallization layer typically composed of a material such as titanium,titanium-tungsten or chromium is deposited on the die. Alternatively, ametal seed layer, such as a copper seed layer, may be deposited on thesemiconductor die to provide metal contact between the copper pillarsand the semiconductor die. After the photosensitive layer has beenremoved from the die, all portions of the underbump metallization layeror seed layer are removed except for the portions underneath thepillars. Conventional processes known in the art may be used.

While the height of the copper pillars may vary, typically they range inheight from 1 μm to 200 μm, preferably from 5 μm to 50 μm, morepreferably from 15 μm to 50 μm. Diameters of the copper pillars may alsovary. Typically the copper pillars have a diameter of 2 μm to 200 μm,preferably from 10 μm to 75 μm, more preferably 20 μm to 25 μm.

The copper electroplating methods and baths provide copper photoresistdefined features which have a substantially uniform morphology and aresubstantially free of nodules. The copper pillars and bond pads have asubstantially flat profile. The copper electroplating baths and methodsenable an average % TIR to achieve the desired morphology as well as abalance between average % TIR and % WID.

The following examples are intended to further illustrate the inventionbut are not intended to limit its scope.

EXAMPLE 1

In 250 mL round-bottom, three-neck flask equipped with a condenser and athermometer, 100 mmol of L-Arginine and 20 mL of deionized (“DI”) waterwere added followed by addition of 100 mmol of glycerol diglycidyl etherat 80° C. The resulting mixture was heated for about 5 hours using anoil bath set to 95° C. and then left to stir at room temperature foradditional 6 hours. The reaction product was transferred into acontainer, rinsed and adjusted with DI water. The reaction productsolution was used without further purification.

EXAMPLE 2

An aqueous acid copper electroplating bath was prepared by combining 40g/L copper ions from copper sulfate pentahydrate, 140 g/L sulfuric acid,50 ppm chloride ion, 5 ppm of an accelerator and 2 g/L of a suppressor.The accelerator was bis(sodium-sulfopropyl)disulfide. The suppressor wasan EO/PO copolymer having a weight average molecular weight of around1,000 and terminal hydroxyl groups. The electroplating bath alsocontained 1 ppm of the reaction product from Example 1. The pH of thebath was less than 1.

A 300 mm silicon wafer segment with a patterned photoresist 50 μm thickand a plurality of apertures (available from IMAT, Inc., Vancouver,Wash.) was immersed in the copper electroplating bath. The anode was asoluble copper electrode. The wafer and the anode were connected to arectifier and copper pillars were electroplated on the exposed seedlayer at the bottom of the apertures. The aperture diameters were 50 μm.Current density during plating was 9 ASD and the temperature of thecopper electroplating bath was at 25° C. After electroplating theremaining photoresist was then stripped with BPR photostripper alkalinesolution available from the Dow Chemical Company leaving an array ofcopper pillars on the wafer. The copper pillars were then analyzed fortheir morphology. The heights and TIR of the pillars were measured usingan optical white light LEICA DCM 3D microscope. The % TIR was determinedby the following equations:% TIR=[height_(center)−height_(edge)]/height_(max)×100,TIR=height_(center)−height_(edge)

The average % TIR of the eight pillars was also determined as shown inthe table.

TABLE 2 Pillar Height_(max) Pillar TIR Pillar # Pitch (μm) (μm) (μm) %TIR 1 100 32.3 −1.0 −3.1 2 100 30.1 −1.2 −4.0 3 100 29.2 −1.4 −4.8 4 10030.2 −1.3 −4.3 5 100 33.8 −1.1 −3.3 6 250 38.8 −0.9 −2.3 7 250 39.2 −1.1−2.8 8 250 37.3 −1.6 −4.3 Avg. — 33.9 −1.2 −3.5%The % WID for the array of pillars was determined with the optical whitelight LEICA DCM 3D microscope and the following equation:% WID=1/2×[(height_(max)−height_(min))/height_(avg)]×100

The average % WID was 14.8% and the average % TR was −3.5%. The surfaceof the pillars all appeared smooth and free of nodules. The copperelectroplating bath which included the reaction product of Example 1plated good copper pillars. FIG. 1 is a 300× AMRAY SEM image of one ofthe pillars plated on a seed layer and analyzed with the opticalmicroscope. The surface morphology was smooth. Although the top or thepillar was slightly dished, the pillar was substantially flat on top forpurposes of solder plating.

EXAMPLE 3

A 300 mm silicon wafer segment with a patterned photoresist 50 μm thickand a plurality of vias (available from IMAT, Inc., Vancouver, Wash.)was immersed in the copper electroplating bath of Example 2. The anodewas a soluble copper electrode. The wafer and the anode were connectedto a rectifier and copper pillars were electroplated on the exposed seedlayer at the bottom of the vias. Current density during plating was 9ASD and the temperature of the copper electroplating bath was at 25° C.

After the wafer was plated with copper pillars, the tops of the copperpillars were then electroplated with a tin/silver solder using SOLDERON™BP TS6000 tin/silver electroplating solution (available from the DowChemical Company, Midland, Mich.). The solder was electroplated up tothe level of the photoresist in each aperture. The photoresist was thenstripped using an alkaline stripper. The silicon wafers were thenreflowed using a Falcon 8500 tool from Sikama International, Inc. having5 heating and 2 cooling zones using temperatures of 140/190/230/230/260°C., with a 30 second dwell time and a conveyor rate of 100 cm/minute anda nitrogen flow rate of 40 cubic feet/hour (approximately 1.13 cubicmeters/hour). ALPA 100-40 flux (Cookson Electronics, Jersey City, N.J.,U.S.A) was the flux used in the reflow. One reflow cycle was done. Afterreflow the eight pillars were cross sectioned using a FIB-SEM and theinterface between the copper pillars and the solder were examined forvoids. Although there were some voids at the interface between thesolder and the copper pillars, there was still good adhesion between thesolder and the copper pillars.

EXAMPLE 4 Comparative

In a 125 mL round-bottom, three-neck flask equipped with a condenser anda thermometer, 90 mmol of 2-methylquinolin-4-amine, 10 mmol of2-(2-aminoethyl)pyridine were added into a mixture of 20 mL of DI waterand 5 ml of 50% sulfuric acid. The mixture was heated to 80° C. followedby drop wise addition of 100 mmol of 1,4-butanediol diglycidyl ether.The resulting mixture was heated for about 4 hours using an oil bath setto 95° C. and then left to stir at room temperature for an additional 8hours. The reaction product (reaction product-comparative) was dilutedwith acidified water and used without further purification.

EXAMPLE 5 Comparative

The method described in Example 2 was repeated with the same copperelectroplating bath, wafer and plating parameters except that reactionproduct-comparative was substituted for the reaction product ofExample 1. Reaction product-comparative was included in the copperelectroplating bath in an amount of 1 ppm. After the wafer was platedwith pillars, the photoresist was stripped leaving an array of copperpillars on the silicon wafer. The pillars appeared rough and many had“sink-hole” centers as shown in FIG. 2. The average % WID and average %TIR were not calculated. The pillars were very defective, thus theprofilometer was unable to read them accurately.

What is claimed is:
 1. A method comprising: a) providing a substratecomprising a layer of photoresist, wherein the layer of photoresistcomprises a plurality of apertures; b) providing a copper electroplatingbath comprising one or more reaction products of one or more α-aminoacids and one or more bisepoxides; an electrolyte; one or moreaccelerators; and one or more suppressors; c) immersing the substratecomprising the layer of photoresist with the plurality of apertures inthe copper electroplating bath; and d) electroplating a plurality ofcopper photoresist defined features in the plurality of apertures, theplurality of photoresist defined features comprise an average % TIR of-5% to -1%.
 2. The method of claim 1, wherein an average % WID of anarray of copper photoresist defined features on the substrate is 12% to15%.
 3. The method of claim 1, wherein the one or more α-amino acids arechosen from arginine and lysine.
 4. The method of claim 1, wherein theone or more bisepoxides have a formula:

wherein R₁ and R₂ are independently chosen from hydrogen and(C₁-C₄)alkyl, A=O((CR₃R₄)_(m)O)_(n) or (CH₂)_(y), each R₃ and R₄ isindependently chosen from hydrogen, methyl, or hydroxyl, m=1-6, n=1-20and y=0-6 and when y=0, A is a chemical bond.
 5. The method of claim 4,wherein the bisepoxides have a formula:

wherein R₁ and R₂ are independently chosen from hydrogen and(C₁-C₄)alkyl, R₃ and R₄ are chosen from hydrogen, methyl or hydroxyl,m=1-6, n=1.
 6. The method of claim 1, wherein the one or more reactionproducts are in amounts of 0.25 ppm to 20 ppm in the copperelectroplating bath.
 7. The method of claim 1, wherein electroplating isdone at a current density of 0.25 ASD to 40 ASD.
 8. The method of claim1, wherein the one or more copper photoresist defined features arepillars, bond pads or line space features.